1. Field of the Invention
The present invention relates to cooling systems for marine vessels, and more specifically, to a closed-loop cooling system for a hydrogen/oxygen based combustor used in an underwater marine vessel.
2. Prior Art
Vehicles that operate underwater are useful for performing tasks below the sea surface in such fields as deep-water salvage operations, navy and marine operations, underwater telecommunications, offshore petroleum and mining, and oceanographic research. Many of these applications are completed by small-scale underwater vehicles that can be either manned or unmanned (robotic or remote controlled). These unmanned vehicles are commonly known as Unmanned Underwater Vehicles (UUVs).
Conventional power systems for these vehicles run an open cycle that consumes some type of fuel and the reaction products are expelled from the vessel. Generally, the traditional combustion systems for these small-scale underwater vessels have used open loop cooling with either air or water. Open loop combustion systems, such as an aircraft or automotive engines, will eject or exhaust the products of the reaction used to generate power.
In the case of an open system such as a missile or torpedo, ejecting mass can be used to generate thrust and propel the vessel. Vessels operating underwater that eject or exhaust mass tend to rise as they become more buoyant. By expelling this mass from the vessel, the vessel becomes more buoyant and tends to rise, thus making it more likely that the vehicle will be spotted or detected. This is a problem for vehicles involved in covert operations. This problem could be mitigated, but it requires complex mechanical systems that significantly increase the associated costs.
Furthermore, the cooling systems for these open-loop combustion systems require outside water, air or other fluids to cool the engines. Modem gas turbine combustion systems have established a number of open loop air-based methods for cooling combustion systems. Additionally, modem gas turbine combustion systems require cooling by active or passive means to absorb and/or redistribute the heat generated by exothermic chemical reactions.
One method for redistributing and utilizing this excess heat is to pass a cooling fluid (gas or liquid) around the combustor to absorb this energy and then inject this fluid into the combustor, in a process known as reverse-flow cooling. In a gas turbine, this has the effect of cooling combustor hardware. Additionally, this fluid can be injected into the combustor to be used as a combustion reactant and/or as a heat sink to reduce flame temperature and/or emissions. These are all open loop methods that eject the cooling fluid from the system.
To eliminate the problem of increasing buoyancy caused by ejecting mass from an open loop system, an underwater vessel could operate with a closed loop power/propulsion system. This limits the amount of mass leaving the vessel and maintains a neutrally buoyant vessel. However, this system would also require a closed loop cooling system. The term closed loop cycle implies that none of the working fluid enters or leaves the power system while in operation. Therefore, there is a need for a closed-loop cooling system for hydrogen/oxygen based combustion systems.